1. Field of the Invention
The present invention relates to an optical pickup assembly, and more particularly, to an optical pickup assembly having an actuator to reduce an eddy current caused by air flow occurring during rotation of a disc.
2. Description of the Related Art
In general, an optical pickup assembly is a device that records and/or reproduces information by radiating light onto a disc (recording medium) through an objective lens and/or by receiving light reflected from the recording medium.
FIG. 1 is an exploded perspective view schematically showing the structure of a conventional optical pickup assembly, FIG. 2 is a side view showing an eddy current occurring in a conventional optical pickup assembly during rotation of a disc, and FIG. 3 is a plane view showing the eddy current shown in FIG. 2.
Referring to FIG. 1, the optical pickup assembly includes: a pickup base 11 installed to slide in a radial direction of a disc; an actuator 12 having a blade 17, which is supported by a plurality of suspensions 15 in a holder 14 fixed in a yoke plate 13, and on which an objective lens 16 is mounted; magnets 18, which are installed on the yoke plate 13 by a predetermined gap and track and/or focus the blade 17; and a cover 19, which is installed to surround the actuator 12, has a hole 19a that is positioned on an upper side of the cover 19, through which light irradiated from the objective lens 16 passes, and which restricts a movement range of the blade 17 in the radial direction of the disc.
The cover 19 restricts the movement range of the blade 17, which is fixedly installed in the yoke plate 13 and moves in the radial direction of the disc by interaction between the cover 19 and the magnets 18. If the optical pickup assembly does not include the cover 19, the objective lens 16 may be damaged while contacting the disc, or a scratch may occur on a surface of the disc.
Referring to FIGS. 2 and 3, information recording and/or reproduction is performed using the optical pickup assembly when the optical pickup assembly makes a reciprocating movement in the radial direction of a disc D while maintaining a predetermined working distance between the disc D and the actuator 12.
Thus, air flow having a uniform speed difference occurs between the disc D and the actuator 12 when the disc D is rotated. In other words, the speed of air adjacent to the disc D is similar to a rotation speed of the disc D, but air speed decreases closer to the actuator 12. The speed difference of the air flow causes an eddy current S on the actuator 12.
As the rotation speed of the disc D increases, a distance between the disc D and the actuator 12 decreases. As a result, the speed of the air flow increases according to Bernoulli's theorem, and the eddy current S increases.
The eddy current flows into the hole 19a positioned on the upper side of the cover 19, and acts on the blade 17 as an asymmetrical force or disturbance. As a result, the blade 17 vibrates upward and downward and disturbs a focusing or tracking operation of the blade 17, so that information recording and/or reproduction is not smoothly performed.
In particular, if a frequency generated by the eddy current S and a natural frequency of the actuator 12 cause resonances, disturbance on the actuator 12 increases.